The present invention relates to a medical instrument, with a cannula through which shafts of other instruments having different shaft diameters can be guided, with a seal comprising an opening with a variable opening cross section through which the shafts having different shaft diameters can be guided sealingly, with an expansion device for expanding the opening of the seal, which expansion device has an expansion cone with a plurality of slats that are mounted pivotably on an annular body and form an expansion body that narrows from the proximal end to the distal end and that is connected to the seal in the area of the opening.
A medical instrument of this kind is known from EP 0 696 459 B1.
Said medical instrument is a trocar that is used in minimally invasive surgery. The trocar is introduced through a small opening, which can be formed by a small incision for example, through the abdominal wall into the abdominal cavity of the patient by means of a trocar mandrel. After removal of the trocar mandrel, shafts of other instruments used for the surgical intervention are then passed through this trocar. These instruments include, for example, gripping tools, coagulation instruments, endoscopes and the like. These have different diameters.
Since minimally invasive interventions of this kind are often performed during insufflation of the internal cavity in which the operation takes place, all the intervention points must be gas-tight.
In the aforementioned EP 0 696 459 B1, this purpose is served by an elastic conical seal that is arranged in the trocar and that narrows from the proximal end to the distal end. To permit uniform widening of the seal when an instrument is inserted into the trocar, the expansion cone is arranged in the proximal direction from this seal. An instrument inserted into the expansion cone expands the latter radially, which widens the opening in the seal. In addition to permitting easier widening of the seal, the expansion cone also prevents damage to the seal during insertion of sharp-edged instruments, because it can be made of a hard material. In this way, the seal is protected by the expansion cone.
To construct the expansion cone, the slats are mounted pivotably at a first end thereof on a ring, as a result of which the conical body of the expansion cone is obtained and the slats can be pivoted radially. For this purpose, they have axial pins at one end, with which the slats have to be engaged pivotably in corresponding recesses in the annular body.
For this purpose, each slat therefore requires exactly shaped endpieces with axial pins. Correspondingly, the annular body must also have exactly shaped engagement means, in addition to which an exactly shaped cover has to be fitted onto the device in order to ensure that the slats do not fall off from the ring. The construction therefore requires a number of exactly produced individual parts with relatively complicated details. This is difficult, especially because of the small size of the components, in the millimeter range, and therefore makes construction complicated. The same also applies to the assembly work in which the very small axial pins have to be engaged in the corresponding recesses in the annular body.
It is therefore an object of the present invention to develop a medical instrument of this kind in such a way that the sealing system is of simpler construction and is less complicated to assemble and less expensive to produce.